Traditional power coupler systems such as on-axis coax or end-butt waveguide systems, are very large in size compared to a single cavity system. When an RF source is powerful enough to drive multiple cavities through the traditional power coupler system at once, this is a small compromise to make. However, when one wishes to drive every cavity independently, with its own RF source or with several sources ganged to a single cavity, these couplers may become impractical.
To make use of an end-butt waveguide coupler, the RE power is typically transferred from a coaxial line to a rectangular waveguide, then passed through a waveguide taper for size constraints, and finally to the cavity. Each transition poses the opportunity for losses and reflections.
Related art loop coupling may be fragile. The loop size is typically defined by the coupling utilized, which in turn, places an upper bound on the size of the conductor used to make the loop, and therefore on its mechanical strength. Further, loops may become increasingly difficult to attach and tune as the cavity size is reduced and frequency increased.